Re: Testing upload/download bandwidth speeds for verification

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On Fri, 2009-08-14 at 09:21 -0700, Daniel B. Thurman wrote:
> > First, the download speed get from any site can only be as high as
> their
> > upload speed.
> >   
> So, does that mean I am wasting money by going from
> 768KB/s Up / 768KB/s Down to 768KB/s Up / 3MB/s
> Down since I will never obtain download speeds faster
> than the Upload limit of 768KB/s ???  The only way to
> get more speed is to increase the Upload speeds to be
> more closer to the Download speeds which is always
> higher?

I suggest you re-read what Ed said, which isn't what you seem to have
understood. Think of it this way: your download is the server's upload.
the maximum bandwidth you can get out of the connection between them is
the lower of these two numbers.

However there are multiple other factors:

* The server usually isn't just serving you, so it's upload speed is
shared among the multiple clients it typically has at a given time.

* You may be using your download link for several other things that you
might not even be aware of, e.g. mail updating, browser page reloads, or
even other parallel downloads (not forgetting other machines on your
local net which share your ISP connection).

* The intermediate connections on the net also have resource
limitations. If one of these is congested, you'll see lower speeds. This
is often the reason for discrepancies between the measured speed of near
and far "speed testing" sites.

* If some connections are unreliable, packets will be retransmitted,
leading to a lower aggregate speed.

* Your link speed (what your ISP sells you) is -- in the best case --
the speed of bits over the wire. Even if they actually give you those
speeds (and there are several reasons why they might not), actual
downloads also have several levels of protocol overhead, so your
end-to-end data transfer will always be less than the rated speed of the
connection, even if all other factors have no effect.

* Lastly, downloads are almost always TCP connections. Every TCP segment
you receive has to be acknowledged by a correspond ACK going the other
way. The ACKs are small relative to the data segments, but they still
use upload bandwidth and this can affect your data throughout.

poc

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